There is a timer before the blizzard appears.
You will have 30 seconds on you to know when the blizzard are going to appear at it's strongest. As you said "because even if you try to pull a perfect flank, a Blizzard can simply come and ruin".
Most likely both players will camp around bonfires with their troops and will be extremely careful with their armor while there's no troops around to defend them.
Therefore you'll have to make the decision between attacking in the blizzard which might come as huge surprise attack and have that as an advantage OR wait till the blizzard is over which makes advantages for both. (Mostly for russian army because of the "Hoorah" abiliy).
Blizzard in my opinon is great and makes the game even more realistic. Deep snow, water, ice, bonfires, everything
